Stray light control in an optical system

Abstract

In an optical system having a mirror system for reflecting light from a field of interest to form a desired image on sensitive material disposed in a focal plane, the improvement characterized by the provision of a centrally located obscuration disposed adjacent the front of a mirror for intercepting light reflected from the sensitive material toward the mirror to prevent reflection from the mirror of said light reflected from the sensitive material from reilluminating the sensitive material, to thereby improve the contrast the desired image.

What is claimed is: 
     
       1. A solid catadioptric photographic system comprising, in combination, a primary mirror for receiving rays of light from a field of interest and reflecting them to a spaced secondary mirror that, in turn, reflects the rays through a central hole in the primary mirror to sensitive material disposed on a focal plane behind said primary mirror, said primary mirror and said secondary mirror being mounted in a tube, an inner primary baffle means mounted adjacent said central hole, a conical secondary baffle mounted adjacent the parameter of said secondary mirror, a series of baffles inwardly directed from the walls of said tube between said primary and said secondary mirrors, and a series of inwardly directed forebaffles mounted on the walls of said tube extending from said secondary mirror towards the field of interest, means for treating the surfaces surrounding the path of the rays of light through the system to substantially reduce specularly the diffusely reflected stray light, a centrally located dark, obscuration disposed adjacent the front of said secondary mirror for intercepting light rays reflected from said sensitive materials towards said secondary mirror to prevent the reflection from said secondary mirror of said light reflected by the sensitive material from forming a secondary image on said sensitive material, the reflection from said sensitive material including a diffuse component and a specular component, the size of said dark obscuration being a function of the flare correction of the light reflected from said sensitive material and the vignetting of useful light, thereby improving the contrast in the desired image on said sensitive material.